CN104192023B - Power demand coupling and the method for optimization during the starting of a kind of pure electric automobile - Google Patents

Abstract

The invention discloses a method for matching and optimizing power demand when a pure electric vehicle starts. According to whether the opening of the accelerator pedal is 0 at the time of starting, the starting of the pure electric vehicle is divided into a starting mode and a driver starting mode; the invention fully considers For each situation that a pure electric vehicle may encounter when starting, combine the starting road conditions, maximum parking gradient requirements, torque fluctuations, starting safety and energy saving and other factors to formulate an optimal control strategy for the starting mode. The reflected starting intention of the driver formulates the fuzzy control strategy of the driver's starting mode, thereby improving the reliability, safety and energy saving of the vehicle.

Description

A method for matching and optimizing power demand when starting a pure electric vehicle

technical field

The invention relates to the technical field of pure electric vehicle drive system control, in particular to the formulation of a starting drive control strategy for pure electric vehicles.

Background technique

The algorithm to realize the control of the vehicle power system is called the driving control strategy, and the driving control strategy is the core content of the pure electric vehicle control system. Since the electric drive control system of pure electric vehicles includes motors, power converters, power batteries, batteries, clutches, transmissions, etc., it is a nonlinear dynamic system integrating electrical, electronic, chemical, and mechanical systems. How to make these components coordinate and effectively Working on the ground is a problem worthy of attention. In addition, different drivers have different driving habits and styles, so they have different demands on the vehicle, which makes it more difficult to judge the driving intention and design the vehicle control strategy.

The starting condition is an important driving condition in the driving conditions of pure electric vehicles, especially when pure electric vehicles are running in urban conditions, nearly 80% of the time is in the starting and acceleration and deceleration conditions. The starting condition is not only related to the road condition, but also closely related to the driver's operation intention. How to comprehensively analyze the starting road condition and the driver's starting intention to formulate the starting control strategy and optimize the starting performance index will affect the driving control of the whole vehicle. An important factor in the effectiveness of system control. Therefore, it is a problem of practical significance to optimize the power demand under the starting condition.

In response to this problem, domestic and foreign scholars have done some research on the power demand matching and optimization of the starting condition. For example: Shanghai Jiaotong University's 2010 master's degree thesis "Research on Control Strategy and Controller of Pure Electric Vehicles", Chongqing University's 2012 master's degree thesis "Pure Electric Vehicle Start Control Strategy Research" separately analyzed the starting conditions, Combining the ramp conditions and the driver's starting intention when the pure electric vehicle starts, a corresponding starting control strategy is formulated. Chongqing University's 2012 master's degree thesis "Research on Vehicle Control Strategy under Electric Vehicle Driving Conditions" used the slope recognition function to formulate control strategies for starting uphill, starting on flat roads, and starting downhill respectively, but did not control driving. The staff started to do research.

The disadvantage of the above method is that it does not fully consider every situation that a pure electric vehicle may encounter when starting, and it is not perfect to formulate a starting control strategy only from a slope start or only from the driver's acceleration intention. It is necessary to comprehensively analyze the starting road conditions and the driver's starting intention to formulate a starting control strategy and optimize the starting performance indicators.

Contents of the invention

In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a method for matching and optimizing the power demand of a pure electric vehicle when starting. By controlling the output torque of the motor, it can fully reflect the driver's starting intention and can well meet the needs of the driver. Different starting road conditions require.

The present invention is achieved through the following technical solutions:

A method for matching and optimizing power demand when starting a pure electric vehicle, dividing the starting of a pure electric vehicle into a starting mode and a driver starting mode according to whether the accelerator pedal opening is 0 when starting;

When the opening of the accelerator pedal is 0, it enters the starting mode, and calculates the basic torque demand of the starting mode according to the maximum stable speed of the starting vehicle;

When the accelerator pedal opening is not 0, enter the driver start mode, and calculate the basic torque demand of the driver start mode according to the relationship curve between the motor output torque and the accelerator pedal opening.

Further, the start-up mode optimizes the basic torque requirements for start-up according to the ramp conditions, maximum parking gradient requirements, torque fluctuations, and start-up safety and energy-saving factors:

When the opening of the brake pedal is reduced to 0.2, the motor should start to provide the output torque Te. At the same time, the output torque should increase continuously with the decrease of the opening of the brake pedal. When the brake pedal is fully released , the motor output torque Te is recorded as holding torque;

When the vehicle starts on a large slope, it is necessary to judge the rotation of the motor rotor. The vehicle needs to perform a self-check on the start of the large slope. Once the motor rotor turns counterclockwise, the motor sensor recognizes the rate of change of the motor speed. Obtain the acceleration of the vehicle's backsliding, identify the acceleration and then obtain the motor torque according to the interpolation method, and control the motor to output the climbing torque under the absolute value of the acceleration through the motor controller. The climbing torque can overcome the slope resistance torque and rolling resistance torque to stop the car from rolling backwards.

When the vehicle speed increases from 0 to the maximum stable speed of 5km/h, large torque fluctuations are caused, which affects ride comfort, and the output torque Te should gradually decrease; when the vehicle speed is detected to be between 5km/h and 8km/h Between , the motor output torque Te should continue to decrease, and when the vehicle speed exceeds 8km/h, the motor output torque Te should gradually decrease to 0.

Further, the climbing torque is greater than the maximum value Ts of the holding torque.

Further, the motor output torque Te in the driver start mode should not be less than the holding torque in the start mode, and the output torque increases linearly with the increase of the accelerator pedal opening to the maximum torque of the motor.

Further, the optimization of the output torque of the motor adopts a fuzzy control algorithm.

Further, the concrete process of adopting the fuzzy control algorithm is as follows:

A. Introducing the rate of change of the accelerator pedal opening combined with the accelerator pedal opening to distinguish the urgency of starting;

B. Establish a fuzzy control strategy to correct the basic starting torque of the driver; multiply the correction coefficient β on the basis of the driver's motor output torque Te to obtain the corrected output torque demand T;

C. The fuzzy controller takes the accelerator pedal opening and its rate of change as input, and the correction coefficient β as the output. The signal of the accelerator pedal opening and its rate of change is collected by the sensor, which is transformed into a fuzzy quantity after fuzzification. During the adjustment process, The linguistic variables of accelerator pedal opening and its change rate and correction coefficient β are selected as: NS, ZO, PS, among which NS and PS are selected as semi-trapezoidal functions, and ZO is selected as triangular membership function.

The beneficial effects of the present invention are: the present invention fully considers every situation that a pure electric vehicle may encounter when starting, divides the starting working condition into a starting mode and a driver starting mode according to the opening of the accelerator pedal, and combines the starting road conditions Formulate an optimal control strategy for the start-up mode based on factors such as the maximum parking gradient requirement, torque fluctuation, safety and energy saving at start, and formulate an optimal control strategy for the driver's start-up mode in combination with the driver's start intention reflected by the accelerator pedal opening and its change rate. By introducing the fuzzy control algorithm to adjust the opening of the accelerator pedal and the rate of change of the opening of the accelerator pedal, the output torque is further optimized, thereby ensuring that the system has a higher ability to deal with nonlinear time-varying, and improving the output torque. The control accuracy and response speed of torque adjustment, the selected membership function and fuzzy control rules can better improve the robustness and adaptability of the system control. Thereby improving the reliability, safety and energy saving of automobile operation.

Description of drawings

Figure 1 is a flow chart of the motor output torque control algorithm under starting conditions.

Figure 2 is the relationship curve between the output torque of the motor and the opening of the brake pedal.

Fig. 3 is the relationship curve between the output torque of the motor and the speed of the vehicle in the starting mode.

Fig. 4 is the fuzzy control calculation method of the torque correction coefficient in the driver's starting mode.

Figure 5 shows the membership function of the accelerator pedal opening.

Fig. 6 is the membership function of the rate of change of the opening degree of the accelerator pedal.

Figure 7 shows the membership function of the correction coefficient β.

Fig. 8 is the fuzzy inference rule of the torque correction coefficient in the driver's starting mode.

detailed description

The present invention will be further described below in conjunction with drawings and embodiments.

The basic idea of the present invention is to divide the starting working condition into the starting mode and the driver starting mode according to the opening of the accelerator pedal, and respectively calculate the Base torque demand for launch mode and driver launch mode. At the same time, the optimal control strategy for the starting mode is formulated based on factors such as starting road conditions, maximum parking gradient requirements, torque fluctuations, starting safety and energy saving, and the driver's starting mode is formulated based on the driver's starting intention reflected by the accelerator pedal opening and its change rate. optimal control strategy.

As shown in Figure 1, when the opening of the accelerator pedal is 0, it enters the starting mode; when the opening of the accelerator pedal is not 0, it enters the driver's starting mode. In the start-up mode, the vehicle will eventually run at a constant speed, which is the maximum stable vehicle speed at start-up. The basic torque requirement in the start-up mode is calculated according to the maximum stable vehicle speed at start-up, as shown in formula 1:

$\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; g</span>}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}}{\mathrm{<span\; class="notranslate">\; Au</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 21.15</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; r</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; \&eta;</span>}}_{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula: m is the unloaded mass of the vehicle, kg; g is the acceleration due to gravity, m/s2; f is the rolling resistance coefficient; CD is the air resistance coefficient; A is the windward area, m2; u is the vehicle speed, m/s; i is the reduction ratio; r is the radius of the vehicle tire, m; ητ is the system efficiency.

In the driver start mode, the motor output torque is related to the accelerator pedal opening in real time, and the basic torque demand of the motor in the driver start mode is calculated according to the relationship curve between the motor output torque and the accelerator pedal opening. The motor output torque Te is as follows: Formula 2 shows:

$\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; =</span>\left\{\begin{array}{cc}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; max</span>}& \mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; e</span>}\\ \mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; 9550</span>}\mathrm{<span\; class="notranslate">\; P</span>}\mathrm{<span\; class="notranslate">\; max</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}& \mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ></span>\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; e</span>}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In the formula: θ(k) is the accelerator pedal opening; Tmax is the maximum output torque of the motor, kw; Pmax is the maximum output power of the motor, kw; n(k) is the actual speed of the motor, r/min; ne is the base speed of the motor , r/min.

On the basis of the traditional control strategy, the start-up performance index is optimized. In the start-up mode, the basic torque requirements for start-up are optimized according to factors such as ramp conditions, maximum parking gradient requirements, torque fluctuations, and start-up safety and energy saving; In the driver start mode, the driver's starting basic torque demand is optimized according to the driver's starting intention reflected by the accelerator pedal opening and its rate of change. Finally determine the driver's torque demand and issue a torque control command to the motor drive system.

As shown in Figure 2, when the vehicle is on the slope with the brake pedal signal, the vehicle will have a tendency to slide down the slope due to the action of gravity. With the release of the brake pedal, the braking force will further decrease. The vehicle will slide downhill. In order to prevent the car from slipping on a slope, when the opening of the brake pedal decreases to a certain value β ₀ (generally 0.2), the motor should start to output torque. When the brake pedal is fully released, the output torque of the motor is the holding torque. This holding torque is linearly dependent on the brake pedal opening during the strategy. When the brake pedal is fully released, the holding torque will reach the maximum value Ts, which is determined by the maximum parking gradient requirement, as shown in formula 3:

$\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; g</span>}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; g</span>}\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; r</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; \&eta;</span>}}_{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In the formula: m is the unloaded mass of the vehicle, kg; g is the acceleration of gravity, m/s2; f is the rolling resistance coefficient; i is the slope; ητ is the system efficiency.

As shown in Figure 3, the maximum stable vehicle speed in the starting mode of the vehicle is 5 km/h, and the basic starting torque Td is calculated based on the maximum stable vehicle speed at starting. Obviously, this torque is smaller than the holding torque when the vehicle speed is 0 , so in order to prevent large torque fluctuations during the process of increasing the vehicle speed from 0 to 5km/h and affecting ride comfort, the output torque should be gradually reduced. In addition, in order to prevent the torque generated by the motor from causing danger due to excessive acceleration of the vehicle when starting downhill, when the vehicle speed is detected to be between 5km/h and 8km/h, the motor torque should be gradually reduced. After the vehicle speed exceeds 8km/h, the motor will no longer work, and this control method can also save energy.

As shown in Figure 4, in order to make the output torque fully reflect the driver’s starting intention, on the basis of the basic output torque Te, the driver’s starting intention is determined according to the accelerator pedal opening and its change rate, and the basic output torque Te is determined by the fuzzy control algorithm. The output torque is optimized. Using the fuzzy control algorithm to develop the motor output torque correction controller with the acceleration pedal opening and its change rate as the input and the correction coefficient as the output. Accelerator pedal opening and its rate of change signals are collected by sensors, and transformed into fuzzy quantities after fuzzification, fuzzy decision-making is made through fuzzy control rules, and then cleared into precise quantities after fuzzy judgment.

Adopt the fuzzy control method shown in accompanying drawing 5-8. It is inaccurate to control the motor output torque only based on the basic torque demand of the driver in the starting mode. When the driver controls the vehicle to start smoothly, a large output torque is not required, so the required torque obtained by the above method is actually If it is too large, it needs to be multiplied by a coefficient to correct the required torque. The fuzzy control algorithm for correcting torque takes the accelerator pedal opening and its change rate as input, and the correction coefficient as the output. Through fuzzification, fuzzy control, defuzzification and other related operations, the correction coefficient β, the accelerator pedal opening and the accelerator pedal opening are calculated. The membership function of degree change rate is shown in Figure 5 and Figure 6, the membership function of correction coefficient β is shown in Figure 7, and the fuzzy inference rule is shown in Figure 8. By multiplying the basic torque demand with the correction coefficient β, the corrected output torque demand can be obtained, and the torque control command can be sent to the motor drive system, so as to realize the optimal control of the power demand of the pure electric vehicle driver's starting mode.

Further, the present invention uses fuzzy control to reason the driver's starting intention. Design the fuzzy controller of the driver's starting intention. The controller system collects the accelerator pedal opening and its change rate signal through the sensor, and converts it into a fuzzy quantity after fuzzification. In order to be precise, the input variable of the controller is the accelerator pedal opening α and its change rate dα/dt, and the output variable is the torque correction coefficient β. As shown in Figure 5-7, the language variables of accelerator pedal opening and its rate of change, correction coefficient are: NS, ZO, PS; domains are 0 to 1, 0 to 8, 0.8 to 1.2, membership degree During the selection process of the function, NS and PS in Fig. 5 to Fig. 7 are selected as semi-trapezoidal functions, ZO is selected as triangular membership function, and the membership functions of the accelerator pedal opening and the rate of change of the accelerator pedal opening are shown in Fig. 5 and Fig. 6, the membership function of the correction coefficient β is shown in Figure 7. According to the driver's operating experience and the torque demand in the actual starting process, the fuzzy rules are formulated as shown in Figure 8. Multiply the motor output torque Te with the correction coefficient β, according to the formula (4), the corrected output torque demand T can be obtained, and the torque control command is sent to the motor drive system, so as to realize the starting mode of the pure electric vehicle driver Optimized control of the power demand.

T=β·Te (4)

By introducing the fuzzy control algorithm to adjust the opening of the accelerator pedal and the rate of change of the opening of the accelerator pedal, the output torque is further optimized, thereby ensuring that the system has a higher ability to deal with nonlinear time-varying, and improving the output torque. The control accuracy and response speed of torque adjustment, the selected membership function and fuzzy control rules can better improve the robustness and adaptability of the system control.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (3)

1. A method for power demand matching and optimization when a pure electric vehicle starts, is characterized in that: whether the accelerator pedal opening is 0 when the pure electric vehicle is started is divided into a starting mode and a driver starting mode; When the opening of the accelerator pedal is 0, it enters the starting mode, and calculates the basic torque demand Td of the starting mode according to the maximum stable speed of the starting vehicle; When the accelerator pedal opening is not 0, enter the driver's starting mode, and calculate the basic torque demand of the driver's starting mode according to the relationship curve between the motor output torque Te and the accelerator pedal opening; The start-up mode optimizes the basic torque requirements for start-up according to the ramp conditions, maximum parking gradient requirements, torque fluctuations, and start-up safety and energy-saving factors: When the brake pedal opening β ₀ decreases to 0.2, the motor should start to provide the output torque Te, and at the same time, the output torque Te should increase continuously with the decrease of the brake pedal opening β ₀ , when braking When the pedal is fully released, the motor output torque Te is recorded as the holding torque; When the vehicle starts on a large slope, it is necessary to judge the rotation of the motor rotor. The vehicle needs to perform a self-check on the start of the large slope. Once the motor rotor turns counterclockwise, the motor sensor recognizes the rate of change of the motor speed. Obtain the acceleration of the vehicle's backsliding, identify the acceleration and then obtain the motor torque according to the interpolation method, and control the motor to output the climbing torque under the absolute value of the acceleration through the motor controller. The climbing torque can overcome the slope resistance torque and rolling resistance torque to stop the car from rolling backwards; When the vehicle speed increases from 0 to the maximum stable speed of 5km/h, large torque fluctuations are caused, which affects ride comfort, and the output torque Te should gradually decrease; when the vehicle speed is detected to be between 5km/h and 8km/h When between, the motor output torque Te should continue to decrease, and when the vehicle speed exceeds 8km/h, the motor output torque Te should gradually decrease to 0; The optimization of the motor output torque Te adopts a fuzzy control algorithm; The concrete process of adopting the fuzzy control algorithm is as follows: A. Introducing the rate of change of the accelerator pedal opening combined with the accelerator pedal opening to distinguish the urgency of starting; B. Establish a fuzzy control strategy to correct the basic starting torque of the driver; multiply the correction coefficient β on the basis of the driver's motor output torque Te to obtain the corrected output torque demand T; C. The fuzzy controller takes the accelerator pedal opening and its rate of change as input, and the correction coefficient β as the output. The signal of the accelerator pedal opening and its rate of change is collected by the sensor, which is transformed into a fuzzy quantity after fuzzification. During the adjustment process, The linguistic variables of accelerator pedal opening and its change rate and correction coefficient β are selected as: NS, ZO, PS, among which NS and PS are selected as semi-trapezoidal functions, and ZO is selected as triangular membership function. 2 . The method for matching and optimizing power demand when starting a pure electric vehicle according to claim 1 , wherein the climbing torque is greater than the maximum value Ts of the holding torque. 3 . 3. The method for power demand matching and optimization when a pure electric vehicle starts according to claim 1, wherein the motor output torque Te under the driver starting mode should not be less than the holding torque under the starting mode, And the output torque Te linearly increases to the maximum torque of the electric motor as the opening of the accelerator pedal increases.